1. Field of the Invention
The present invention relates in general to automatically focusable video cameras, and more particularly to an apparatus and a method for automatically focusing an object in a video camera portion of a camcorder in which a motion speed of a video camera lens is controlled according to a slope of video detect data and the motion of the tens is stopped before a level of the video detect data reaches a peak value, so that an overshoot at the peak value can prevented and the object can be focused at a high speed.
2. Description of the Prior Art
Referring to FIG. 1, there is shown a block diagram of a conventional apparatus for automatically focusing an object in a video camera portion of a camcorder. As shown in this drawing, the conventional automatic focusing apparatus comprises a lens 1 for receiving a light beam from the object, an iris 2 for adjusting an amount off the light beam being received by the lens 1, a solid state image sensor 3 for converting the light beam of the amount adjusted by the iris 2 into an electrical signal and outputting the resultant video signal, an amplifier 4 for amplifying the video signal from the solid state image sensor 3, and a video signal processor 5 for processing the video signal amplified by the amplifier 4 so that the amplified video signal can be displayed on a screen.
Band pass filters (BPFs) 6 and 7 are provided in the conventional automatic focusing apparatus to filter the video signal amplified by the amplifier 4 at different frequency bands, respectively.
A video divider 8 is also provided in the conventional automatic focusing apparatus to divide the video signals filtered by the band Lass filters 6 and 7 in the unit of field to find the object to be focused.
The conventional automatic focusing apparatus also comprises an analog/digital (A/D) converter 9 for converting the video signals divided by the video divider 8 into digital signals an integrator 10 for integrating the digital signals from the A/D converter 9 to output video detect data for focusing the object, a main microprocessor 11 for outputting a focusing control signal in accordance with a level of the video detect data from the integrator 10, and a motor drive microprocessor 12 for outputting a control signal in response to the focusing control signal from the main microprocessor 11 to drive a lens motor driver 13.
The operation off the conventional automatic focusing apparatus with the above-mentioned construction will hereinafter be described.
First, the light beam from the object is received by the lens 1, the amount thereof being adjusted by the iris 2. The light beam of the amount adjusted by the iris 2 is converted into the electrical signal by the solid state image sensor 3. As a result, the video signal is generated from the solid state image sensor 3.
The video signal from the solid state image sensor 3 is amplified by the amplifier 4 and then processed by the video signal processor 5 so that it can be displayed on the screen. The video signal amplified by the amplifier 4 is also applied to the band pass filter 6.
In an initial focusing state, the video signal amplified by the amplifier 4 is filtered by the band pass filter 6 at the frequency band as shown in FIG. 3, which is a graph illustrating focusing steps which are performed by a conventional method of automatically focusing the object in the camcorder. The filtered video signal is divided in the unit of field by the video divider 8 for finding the object to be focused. The divided video signals are converted into the digital signals by the A/D converter 9 and then integrated by the integrator 10. As a result, the video detect data for focusing the object is generated from the integrator 10. The video detect data from the integrator 10 is applied to the main microprocessor 11.
The main microprocessor 11 analyzes the video detect data from the integrator 10 and checks a motion of the object to be focused, in accordance with the analyzed result. If the object has been moved, the main microprocessor 11 outputs the focusing control signal to move the lens 1 to a moved position of the object. The focusing control signal from the main microprocessor 11 is applied to the motor drive microprocessor 12.
In response to the focusing control signal from the main microprocessor 11, the motor drive microprocessor 12 detects the level of the video detect data and outputs the control signal to the lens motor driver 13 in accordance with the detected level of the video detect data to move the lens 1. Namely, the motor drive microprocessor 12 outputs the control signal to move the lens 1 to a position at which the level of the video detect data is increased.
The operation of the motor drive microprocessor 12 will hereinafter be described in detail with reference to FIG. 2 which is a flowchart illustrating the conventional method of automatically focusing the object in the camcorder.
First, the motor drive microprocessor 12 checks whether the video detect data is focusable stable data. If the video detect data is the focusable stable data, the motor drive microprocessor 12 outputs the control signal to the lens motor driver 13 to move the lens 1 by a desired distance. As a result, the lens 1 is moved by the lens motor driver 13 in response to the control signal from the motor drive microprocessor 12.
As the lens 1 is moved, new video detect data is applied to the motor drive microprocessor 12. The motor drive microprocessor 12 compares a level of the present video detect data with that of the previous video detect data. If the level of the present video detect data is greater than that of the previous video detect data, the motor drive microprocessor 12 outputs the control signal to move the lens 1 in the same direction as the present motion direction. On the contrary, if the level of the present video detect data is not greater than that of the previous video detect data, the motor drive microprocessor 12 outputs the control signal to move the lens 1 in the opposite direction to the present motion direction.
The above operation is repeatedly performed until the Level of the video detect data reaches a peak value at which the object is focused. After reaching the peak value, the level of the present video detect data becomes lower than that of the previous video detect data.
Then, the motor drive microprocessor 12 compares the level of the present video detect data with a predetermined threshold value. If the Level of the present video detect data is lower than the predetermined threshold, the motor drive microprocessor 12 outputs the control signal to move the lens 1 in the opposite direction to the present motion direction. On the contrary, if the level of the present video detect data is not lower than the predetermined threshold, the motor drive microprocessor 12 outputs the control signal to move the lens 1 in the same direction as the present motion direction until the level of the present video detect data becomes lower than that of the predetermined threshold value.
At this time, a counting operation is performed to count steps by which the lens 1 is moved until the level of the video detect data reaches the predetermined threshold value via the peak value. As a result, the lens 1 is moved by the counted value to focus the object.
Thereafter, the motor drive microprocessor 12 checks whether the object to be focused has been moved. If the object has been moved, the motor drive microprocessor 12 moves the lens 1 to a moved position of the object through the above operation to focus the object.
However, the above-mentioned conventional automatic focusing apparatus has a disadvantage in that the construction is complex since the separate motor drive microprocessor is required to control the lens drive motor. Also, in order to accurately focus the object, the lens must be again moved to the peak value after passing the peak value. This results in generation of an overshoot at the peak value. The generation of the overshoot results in a difficulty in obtaining a high picture quality. Further, because the lens is moved at a constant speed, it takes a long time to focus the object.